The long term goal of this proposal is to elucidate the molecular structures on heart cells that function as receptors for Trypanosoma cruzi. T. cruzi is the causative agent of Chagas' disease, a heart disease that affects millions of people in South and Central America. The major target of this blood parasite is the heart tissue, causing cardiac arrest which is frequently accompanied by death. Increasing cases of Chagas' disease transmitted by blood transfusions have been reported in the United States and despite the mortality and morbidity attributed to this blood parasite very little is known, if any, about host cell receptors for T. cruzi. We have found that the purified surface 74 kDa glycoprotein from heart myoblasts and antibodies specific to this molecule inhibit T. cruzi trypomastigote binding and internalization into heart myoblasts. This glycoprotein binds to invasive trypomastigote but not to non-invasive epimastigote forms of T. cruzi and is expressed on cells that can be invaded by trypomastigotes but not on cells that can not be invaded by this form of the parasite. In view of these findings, we have hypothesized that the host 74 kDa glycoprotein may function as a receptor for T. cruzi. In this proposal we will test this hypothesis and we will learn its molecular structure. To this end, we propose the following specific aims: a) to identify clones expressing the 74 kDa protein from an expression cDNA library of mouse heart cells, clone the human protein from a human heart cDNA library and obtain DNA sequencing information from both DNA inserts encoding the 74 kDa protein and predict their amino acid sequence, b) to express and purify the recombinant 74 kDa protein for ligand binding studies to trypanosomes, and c) to test the ability of the 74 kDa protein to function as a receptor for T. cruzi by transfecting mammalian cell lines which can not be invaded by T. cruzi. It is anticipated that this proposal would generate new information and insights about the molecular structure of membrane protein present on heart cells that may function as a receptor for this blood and heart tissue parasite. In addition, these studies will serve as a model to study the role of mammalian surface proteins as receptors for other blood and tissue parasites that may play an important role in cell-parasite recognition. The significance of these studies is that they will contribute to the establishment of the molecular basis of T. cruzi recognition by heart cells that promotes trypanosome entry. This information is very much needed for molecular intervention in this heart disease.